use std::ops::Deref;

static S0: &[u8] = &[
    0x3E, 0x72, 0x5B, 0x47, 0xCA, 0xE0, 0x00, 0x33, 0x04, 0xD1, 0x54, 0x98, 0x09, 0xB9, 0x6D, 0xCB,
    0x7B, 0x1B, 0xF9, 0x32, 0xAF, 0x9D, 0x6A, 0xA5, 0xB8, 0x2D, 0xFC, 0x1D, 0x08, 0x53, 0x03, 0x90,
    0x4D, 0x4E, 0x84, 0x99, 0xE4, 0xCE, 0xD9, 0x91, 0xDD, 0xB6, 0x85, 0x48, 0x8B, 0x29, 0x6E, 0xAC,
    0xCD, 0xC1, 0xF8, 0x1E, 0x73, 0x43, 0x69, 0xC6, 0xB5, 0xBD, 0xFD, 0x39, 0x63, 0x20, 0xD4, 0x38,
    0x76, 0x7D, 0xB2, 0xA7, 0xCF, 0xED, 0x57, 0xC5, 0xF3, 0x2C, 0xBB, 0x14, 0x21, 0x06, 0x55, 0x9B,
    0xE3, 0xEF, 0x5E, 0x31, 0x4F, 0x7F, 0x5A, 0xA4, 0x0D, 0x82, 0x51, 0x49, 0x5F, 0xBA, 0x58, 0x1C,
    0x4A, 0x16, 0xD5, 0x17, 0xA8, 0x92, 0x24, 0x1F, 0x8C, 0xFF, 0xD8, 0xAE, 0x2E, 0x01, 0xD3, 0xAD,
    0x3B, 0x4B, 0xDA, 0x46, 0xEB, 0xC9, 0xDE, 0x9A, 0x8F, 0x87, 0xD7, 0x3A, 0x80, 0x6F, 0x2F, 0xC8,
    0xB1, 0xB4, 0x37, 0xF7, 0x0A, 0x22, 0x13, 0x28, 0x7C, 0xCC, 0x3C, 0x89, 0xC7, 0xC3, 0x96, 0x56,
    0x07, 0xBF, 0x7E, 0xF0, 0x0B, 0x2B, 0x97, 0x52, 0x35, 0x41, 0x79, 0x61, 0xA6, 0x4C, 0x10, 0xFE,
    0xBC, 0x26, 0x95, 0x88, 0x8A, 0xB0, 0xA3, 0xFB, 0xC0, 0x18, 0x94, 0xF2, 0xE1, 0xE5, 0xE9, 0x5D,
    0xD0, 0xDC, 0x11, 0x66, 0x64, 0x5C, 0xEC, 0x59, 0x42, 0x75, 0x12, 0xF5, 0x74, 0x9C, 0xAA, 0x23,
    0x0E, 0x86, 0xAB, 0xBE, 0x2A, 0x02, 0xE7, 0x67, 0xE6, 0x44, 0xA2, 0x6C, 0xC2, 0x93, 0x9F, 0xF1,
    0xF6, 0xFA, 0x36, 0xD2, 0x50, 0x68, 0x9E, 0x62, 0x71, 0x15, 0x3D, 0xD6, 0x40, 0xC4, 0xE2, 0x0F,
    0x8E, 0x83, 0x77, 0x6B, 0x25, 0x05, 0x3F, 0x0C, 0x30, 0xEA, 0x70, 0xB7, 0xA1, 0xE8, 0xA9, 0x65,
    0x8D, 0x27, 0x1A, 0xDB, 0x81, 0xB3, 0xA0, 0xF4, 0x45, 0x7A, 0x19, 0xDF, 0xEE, 0x78, 0x34, 0x60,
];

static S1: &[u8] = &[
    0x55, 0xC2, 0x63, 0x71, 0x3B, 0xC8, 0x47, 0x86, 0x9F, 0x3C, 0xDA, 0x5B, 0x29, 0xAA, 0xFD, 0x77,
    0x8C, 0xC5, 0x94, 0x0C, 0xA6, 0x1A, 0x13, 0x00, 0xE3, 0xA8, 0x16, 0x72, 0x40, 0xF9, 0xF8, 0x42,
    0x44, 0x26, 0x68, 0x96, 0x81, 0xD9, 0x45, 0x3E, 0x10, 0x76, 0xC6, 0xA7, 0x8B, 0x39, 0x43, 0xE1,
    0x3A, 0xB5, 0x56, 0x2A, 0xC0, 0x6D, 0xB3, 0x05, 0x22, 0x66, 0xBF, 0xDC, 0x0B, 0xFA, 0x62, 0x48,
    0xDD, 0x20, 0x11, 0x06, 0x36, 0xC9, 0xC1, 0xCF, 0xF6, 0x27, 0x52, 0xBB, 0x69, 0xF5, 0xD4, 0x87,
    0x7F, 0x84, 0x4C, 0xD2, 0x9C, 0x57, 0xA4, 0xBC, 0x4F, 0x9A, 0xDF, 0xFE, 0xD6, 0x8D, 0x7A, 0xEB,
    0x2B, 0x53, 0xD8, 0x5C, 0xA1, 0x14, 0x17, 0xFB, 0x23, 0xD5, 0x7D, 0x30, 0x67, 0x73, 0x08, 0x09,
    0xEE, 0xB7, 0x70, 0x3F, 0x61, 0xB2, 0x19, 0x8E, 0x4E, 0xE5, 0x4B, 0x93, 0x8F, 0x5D, 0xDB, 0xA9,
    0xAD, 0xF1, 0xAE, 0x2E, 0xCB, 0x0D, 0xFC, 0xF4, 0x2D, 0x46, 0x6E, 0x1D, 0x97, 0xE8, 0xD1, 0xE9,
    0x4D, 0x37, 0xA5, 0x75, 0x5E, 0x83, 0x9E, 0xAB, 0x82, 0x9D, 0xB9, 0x1C, 0xE0, 0xCD, 0x49, 0x89,
    0x01, 0xB6, 0xBD, 0x58, 0x24, 0xA2, 0x5F, 0x38, 0x78, 0x99, 0x15, 0x90, 0x50, 0xB8, 0x95, 0xE4,
    0xD0, 0x91, 0xC7, 0xCE, 0xED, 0x0F, 0xB4, 0x6F, 0xA0, 0xCC, 0xF0, 0x02, 0x4A, 0x79, 0xC3, 0xDE,
    0xA3, 0xEF, 0xEA, 0x51, 0xE6, 0x6B, 0x18, 0xEC, 0x1B, 0x2C, 0x80, 0xF7, 0x74, 0xE7, 0xFF, 0x21,
    0x5A, 0x6A, 0x54, 0x1E, 0x41, 0x31, 0x92, 0x35, 0xC4, 0x33, 0x07, 0x0A, 0xBA, 0x7E, 0x0E, 0x34,
    0x88, 0xB1, 0x98, 0x7C, 0xF3, 0x3D, 0x60, 0x6C, 0x7B, 0xCA, 0xD3, 0x1F, 0x32, 0x65, 0x04, 0x28,
    0x64, 0xBE, 0x85, 0x9B, 0x2F, 0x59, 0x8A, 0xD7, 0xB0, 0x25, 0xAC, 0xAF, 0x12, 0x03, 0xE2, 0xF2,
];

static D: &[u16] = &[
    0x44D7, 0x26BC, 0x626B, 0x135E, 0x5789, 0x35E2, 0x7135, 0x09AF, 0x4D78, 0x2F13, 0x6BC4, 0x1AF1,
    0x5E26, 0x3C4D, 0x789A, 0x47AC,
];

#[inline]
fn u31_add(a: u32, b: u32) -> u32 {
    let c = u32::wrapping_add(a, b);
    (c & 0x7FFFFFFF) + c.wrapping_shr(31)
}

#[inline]
fn u31_rotl(a: u32, shift: u32) -> u32 {
    (a.wrapping_shl(shift) | a.wrapping_shr(31 - shift)) & 0x7FFFFFFF
}

#[inline]
fn l1(x: u32) -> u32 {
    x ^ x.rotate_left(2) ^ x.rotate_left(10) ^ x.rotate_left(18) ^ x.rotate_left(24)
}

#[inline]
fn l2(x: u32) -> u32 {
    x ^ x.rotate_left(8) ^ x.rotate_left(14) ^ x.rotate_left(22) ^ x.rotate_left(30)
}

#[inline]
fn mk_u31(a: u8, b: u16, c: u8) -> u32 {
    (u32::from(a).wrapping_shl(23) | u32::from(b).wrapping_shl(8) | u32::from(c)) & 0x7FFFFFFF
}

#[inline]
fn sbox(x: u32) -> u32 {
    let [a, b, c, d] = x.to_be_bytes().map(usize::from);
    let [a, b, c, d] = [S0[a], S1[b], S0[c], S1[d]];
    u32::from_be_bytes([a, b, c, d])
}

struct Lfsr {
    lfsr: [u32; 16],
}

impl Deref for Lfsr {
    type Target = [u32; 16];

    fn deref(&self) -> &Self::Target {
        &self.lfsr
    }
}

impl Lfsr {
    fn new(key: [u8; 16], iv: [u8; 16]) -> Self {
        let lfsr = std::array::from_fn(|i| mk_u31(key[i], D[i], iv[i]));
        Lfsr { lfsr }
    }

    fn init(&mut self, u: u32) {
        self.append(u31_add(self.next(), u));
    }

    fn append(&mut self, mut f: u32) {
        if f == 0 {
            f = 0x7FFFFFFF;
        }
        self.lfsr.rotate_left(1);
        self.lfsr[15] = f;
    }

    fn next(&self) -> u32 {
        let f = self.lfsr[0];
        let f = u31_add(f, u31_rotl(self.lfsr[0], 8));
        let f = u31_add(f, u31_rotl(self.lfsr[4], 20));
        let f = u31_add(f, u31_rotl(self.lfsr[10], 21));
        let f = u31_add(f, u31_rotl(self.lfsr[13], 17));
        let f = u31_add(f, u31_rotl(self.lfsr[15], 15));
        f
    }

    fn shift(&mut self) {
        self.append(self.next());
    }
}

fn to_be_u32(bytes: &[u8]) -> impl Iterator<Item = u32> + '_ {
    bytes
        .chunks(4)
        .map(TryInto::try_into)
        .map(Result::unwrap)
        .map(u32::from_be_bytes)
}

fn to_be_u32_pkcs7_padding(bytes: &[u8]) -> impl Iterator<Item = u32> + '_ {
    bytes
        .chunks(4)
        .map(|chunk| {
            let mut buffer = [0; 4];
            buffer[..chunk.len()].copy_from_slice(chunk);
            buffer[chunk.len()..].fill((4 - chunk.len()) as u8);
            u32::from_be_bytes(buffer)
        })
        .chain((bytes.len() % 4 == 0).then_some(0x04040404))
}

fn remove_pkcs7_padding(mut bytes: Vec<u8>) -> Vec<u8> {
    let padding = bytes.last().copied().unwrap_or_default() as usize;
    bytes.truncate(bytes.len() - padding);
    bytes
}

pub struct Zuc {
    r0: u32,
    r1: u32,
    lfsr: Lfsr,
}

impl Zuc {
    pub fn new(key: [u8; 16], iv: [u8; 16]) -> Self {
        let mut zuc = Zuc {
            r0: 0,
            r1: 0,
            lfsr: Lfsr::new(key, iv),
        };
        for _ in 0..32 {
            let [x0, x1, x2, _] = zuc.bit_reorganization();
            let w = zuc.f(x0, x1, x2);
            zuc.lfsr.init(w.wrapping_shr(1));
        }
        zuc
    }

    fn processs(&mut self, input: impl Iterator<Item = u32>) -> Vec<u8> {
        let [x0, x1, x2, _] = self.bit_reorganization();
        self.f(x0, x1, x2); // Discard the output of F.

        input
            .map(|i| i ^ self.zuc())
            .flat_map(u32::to_be_bytes)
            .collect()
    }

    pub fn encrypt(mut self, input: &[u8]) -> Vec<u8> {
        self.processs(to_be_u32_pkcs7_padding(input))
    }

    pub fn decrypt(mut self, input: &[u8]) -> Vec<u8> {
        remove_pkcs7_padding(self.processs(to_be_u32(input)))
    }

    fn zuc(&mut self) -> u32 {
        self.lfsr.shift();
        let [x0, x1, x2, x3] = self.bit_reorganization();
        self.f(x0, x1, x2) ^ x3
    }

    fn bit_reorganization(&mut self) -> [u32; 4] {
        [
            (self.lfsr[15] & 0x7FFF8000).wrapping_shl(1) | (self.lfsr[14] & 0xFFFF),
            self.lfsr[11].wrapping_shl(16) | self.lfsr[9].wrapping_shr(15),
            self.lfsr[7].wrapping_shl(16) | self.lfsr[5].wrapping_shr(15),
            self.lfsr[2].wrapping_shl(16) | self.lfsr[0].wrapping_shr(15),
        ]
    }

    fn f(&mut self, x0: u32, x1: u32, x2: u32) -> u32 {
        let w = (x0 ^ self.r0).wrapping_add(self.r1);
        let w1 = u32::wrapping_add(self.r0, x1);
        let w2 = self.r1 ^ x2;
        self.r0 = sbox(l1(w1.wrapping_shl(16) | w2.wrapping_shr(16)));
        self.r1 = sbox(l2(w2.wrapping_shl(16) | w1.wrapping_shr(16)));
        w
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[track_caller]
    fn test_case(key: [u8; 16], iv: [u8; 16], plaintext: &[u8]) {
        let encrypted = Zuc::new(key, iv).encrypt(plaintext);
        let decrypted = Zuc::new(key, iv).decrypt(&encrypted);
        assert_eq!(plaintext, &decrypted);
    }

    #[test]
    fn test_encrypt_decrypt() {
        let key = [0u8; 16];
        let iv = [1u8; 16];
        test_case(key, iv, b"Hello, world!");
        test_case(key, iv, "特朗普".as_bytes());
        test_case(key, iv, "境外势力".as_bytes());
    }
}
